(1) Field of the Invention
The present invention relates to an optical coupler comprising N number of optical fibers. More particularly, the present invention relates to an optical coupler comprising N number of optical fibers and N number of integrally assembled optical coupler parts, each optical fiber comprising an optical fiber-coupling portion having a coupling angle to the optical fiber axis of .theta. and including 1 or 2 planes of 360.degree./N and an optical fiber-connecting end face, and each coupler part having a retention hole for retaining the optical fiber therein, a plane of which is the same as the 1 or 2 planes crossed at the angle of 360.degree./N at the optical fiber-connecting portion and a plane vertical to the 1 or 2 planes, which coupler is particularly applicable to the branching or transmitting of optical signals to a plurality of points in an optical network.
(2) Description of the Related Art
An optical coupler for branching optical signals from an optical signal generator to a plurality of receivers through optical fibers or coupling optical signals from transmitters in an optical network has been developed. For example, Japanese Unexamined Patent Publication No. 63-6049 discloses an optical coupler comprising one light-transmitting optical fiber and a plurality of branching core-clad optical fibers connected to the light-transmitting fiber, in which a branching or coupling of the optical signals is effected between these optical fibers. As shown in FIG. 9, illustrating a light-branching coupler of this type, each of N number, for example, four, of branching optical fibers in the light-branching and coupling end portion is processed so that the end portion of each optical fiber has two planes 91 and 92 having an angle of 360.degree./N (=4), and as shown in FIG. 10, the intersection lines 93 of the two planes of each of the optical fibers 102, 103, 104, and 105 are superimposed on each other to form an integrated end portion, and the end of a light-transmitting optical fiber 106 is connected to this integrated end portion through a sleeve 101 for effecting a branching and coupling of optical signals.
Since the branching-coupling end of each light-branching optical fiber used in the optical coupler of this type has an end comprising two planes 91 and 92 having an angle of 360.degree./N (N being for example, 4), this optical fiber is prepared by cutting the end of a starting optical fiber by a cutter and polishing the cut end face by a polisher. However, according to this method, a precise processing of the end face of the optical fiber is difficult and a deviation of the angle at the end of the optical fiber is large. Accordingly, when a light-branching optical fiber is assembled as shown in FIG. 10, it is impossible to attain a satisfactory light branching-coupling efficiency in the assembled optical coupler, and therefore, the optical coupler of this type is unsatisfactory from the practical view-point.
Moreover, since connection of N number of end face-processed optical fibers 102, 103, 104, and 105 to one optical fiber 106 is effected through the sleeve 101, the mechanical strength of the light branching-coupling portion may be weakened and the light branching-coupling property become unsatisfactory.